1. Field of the Invention
The present invention relates to an optical scanning device which is capable of reading image information from a document and which is used in a laser beam printer for writing images by electrophotographic processes.
2. Description of the Related Art
There has been known an image reading optical device capable of reading an entire image from a document. The image reading optical device first irradiates the document surface with fluorescent light, for example. Light reflected from the document surface is guided toward a line sensor by a reducing projection lens. The line sensor is comprised of a charge-coupled device (CCD) extending in a main scanning direction. Detection signals outputted from the line sensor represent a single line's worth of image of the document. The document surface is scanned in an auxiliary scanning direction orthogonal to the main scanning direction, thereby obtaining image information of the entire document.
There has also been known an image writing optical device. In the image writing optical device, a polygon mirror is rotatingly provided to scan a photosensitive layer on the surface of a photosensitive drum in a main scanning direction. The main scanning direction extends parallel with an axis of the photosensitive drum. The photosensitive drum rotates about its axis in an auxiliary scanning direction so that a latent image is formed on the photosensitive layer. The latent image is then developed into a toner image through a predetermined electrophotographic process. That is, toner is supplied from a developing unit and selectively attached onto the surface of the photosensitive drum. A transferring unit transfers the toner image onto a recording sheet. A fixing unit fixes the transferred toner image onto a recording sheet.
Japanese Laid-Open Patent Application No. HEI-7-199097 discloses another device which has both an image reading function and an image writing function. This device uses optical components common to perform both an image reading operation and an image writing operation.